Project Sunrise Los Angeles California 1974 Flight of the Worlds First Solar Powered Aircraft by Roland Boucher
Chapter 1 Background
In November 1970 I began to investigate the possibility of flying a radio controlled model aircraft on electric power. The basic equations of flight revealed that “off the shelf” nickel cadmium batteries had more than enough energy density to fly a practical RC model plane and they could be recharged in 15 minutes. In April 1971 I demonstrated my first electric model plane at a trade show in Anaheim, California.
Later in the year I contacted the Eagle-Pitcher Corp. asking them to donate one of their high energy silver zinc batteries for an experiment to replace the VW engine in a Fournier RF4 powered sailplane with an electric motor and batteries. They declined but promised to give me a smaller non rechargeable version of the battery for experimentation.
I built a six foot span semi-scale model of an RF4 using this battery. The model flew on Feb 4, 1972 demonstrating that an electric powered plane could fly for one hour at an average speed of 50 mph. This flight led to a proposal to build an 8 foot span, 25 pound battlefield drone which would fly for one hour on silver zinc rechargeable batteries and carry a five pound payload. In early 1973 I conceived of a high altitude unmanned aircraft with unlimited duration which would be powered by the sun.
Above,The author holding a plaque depicting the patent he was awarded in 1976 for the invention of a radio controlled electric airplane
Chapter 2 The Concept
The sun irradiates the earth with a tremendous amount of energy each day. This energy, if converted to mechanical power is more than enough to fly a light weight aircraft. For example, on December 17, 1903 the Wright Brothers flew the worlds first airplane at Kitty Hawk North Carolina using a 12 HP gasoline engine. At noon that day the solar radiation received by the 255 square foot top wing would have been over 12KW (16HP ). If they had flown on June 21 the wing would have received 24 KW of solar power
The Level of Solar Energy Impinging on a Flat Surface at Sea Level.
Solar cell technology in 1973 was capable of achieving efficiency levels of about 17%, today in 2009 levels of nearly 40 percent are possible. Project Sunrise would use garden variety cells with 10% efficiency which would limit electrical power to about 500 watts.
The Minimum Power Required for Level Flight
The power required to fly an aircraft can be calculated from a few simple equations.Power is in foot-lbs/sec, thrust in pounds, velocity in feet /sec, and wing loading in pounds/sq ft. Ar is the aspect ratio of the wing, Cd the coefficient of drag , and Cl the coefficient of lift of theselected airfoil. The bracket amount on line 5 is a square root.
The Factor in the bracket is shown below for an Eppler 387 airfoil operating at a Reynolds number of 100,000. Other Drag is that from the fuselage and tail and is assumed to be 20% of the wing at a lift coefficient of 1.0. Induced drag due to lift is assumed to be CL2/πAr.
A minimum value for the Factor of 0.19 will be used in our analysis.
6 minimumpower = (29x0.190)W3/2/b = 5.5W3/2 /b ftlbs/sec
7 minimum power = 7.5 W3/2 / b watts
8 Climb rate hc = ΔP/ W = 44 ft per minute per watt/lb
DARPA instructed us to select a wing span of 32 feet for the demonstration model of the proposed 100 foot span Solar powered high altitude drone. The proposal called for a wing loading of 4 oz per square foot and an aspect ratio of 12:1. This yielded a wing area of 85.33 square feet and a gross weight of 21.33 pounds. A lift coefficient of 0.9 was selected for both climb and glide.
From equation 6 minimum power = 5.5 x( 98.5 / 32 ) = 16.92 ft lbs /sec
From equation 7 minimum power = 22.94 watts
From equation 3 Velocity = 15.28 fps = 10.4 mph
From equation 2 Thrust = 16.92/15,28 = 1.107 pounds
Solar radiation at noon on June 21 in the Los Angeles area reaches a maximum of 900 watts per square meter. At noon our 85.33 square foot wing would receive about 7850 watts of solar radiation. If all this power were converted to useful thrust through perfect 100% efficient solar cells, motor, and propeller, the climb rate from equation 8 would be 16,193 feet per minute and our perfect plane would reach 73,000 feet in less than 5 minutes.
From equation 8 Climb Rate = (44 /21.33) x 7850 = 16,193 feet per minute
Today, in 2009, Solar cells can approach an efficiency of 40%, brushless motors and modern propellers can each approach 90% efficiency. Our nearly perfect plane would generate 3140 watts of electrical power, the 2543 watts of thrust power would result in a climb rate of 5245 feet per minute.
In 1973 real life losses were expected to be much larger:
1 Economical and available solar cells were only 10 percent efficient.
2 Solar were restricted to the aft 2/3 of the wing surface.
3 Economical circular cells were used which lost 26% of available area.
Our 7850 watts of solar radiation would now produce only 445 watts of electrical power. Project Sunrise, in the initial flight test on battery power, used two commercial servo motors to drive the propeller through a 6:1 speed reducer. All flights under solar power used a single motor which used high energy Samarium Cobalt magnets. This breakthrough motor produced the same power at half the weight and operated at 85% efficiency.
In order to determine the climb and glide profile of Project Sunrise we will have to correct both the airspeed and propeller speeds for the effect of reduced air density at altitude. the power required for level flight will increase directly with the increase in airspeed requiring a 400 percent increase in minimum power at the design altitude of 73,000 feet.
The propeller speed will also increase about 250 percent over the sea level value in the thin upper atmosphere as shown below. The thrust power required for level flight at the design altitude of 73,000 feet is four times the power at sea level.
The propeller chosen for Project Sunrise had an expected efficiency of 60% at sea level rising to 73% at the design altitude of 73,000 feet.
The minium power required for level flight both at sea level and at design altitude as well as the climb rate for both altitudes are as follows:
Min Power at seal level = 23 / (0.85 X 0.60) = 45 watts
Min power at 73000 ft = 23 X 4/( 0.85X 0.73) = 148 watts
Climb Rate at noon, sea level = (445–45) x (44/21.33) x 0.85 x 0.60) = 421 fpm
Climb Rate at noon, 73000 ft = (445–148) x (44/21.33) x o,85 x 0.73) = 380 fpm
The choice of propeller was limited by the motor speed (RPM) and the drive belt speed reduction available. The figure at the right shows the expected efficiency of the propeller chosen.
The power available to climb the aircraft as a function of time of day and altitude is shown at the right. Propeller efficiency was assumed to remain at 60% for these calculations.
The following tables show possible climb and glide profiles.
Lift off time of 7:00 AM was chosen to provide an initial climb rate of 150 fpm.
Climb profile for Project Sunrise at 21.33 pounds and 445 watts at noon on June 21
There will be a loss of power as the sun goes down, and the propeller efficiency will be about 20% better than this table assumed when the aircraft is above 73,000 feet. Nevertheless we will assume that the aircraft will begin a gliding descent one hour later at 4:00 PM
Sink speed can be determined from the minimum power (6) and glide power equation 9:
9 Glide power = sink rate x weight ft lbs /sec
10 Sink rate = 5.5 W1/2/b = 5.5 x 4.62/32 = 0.794 feet /sec = 47.6 fpm
Glide profile at altitude for aircraft with sink speed of 47.6 fpm at sea level
The next section of this report will describe the design, construction and flight test of the first prototype of Project Sunrise, the worlds first solar powered plane.
Chapter 3 Design, Construction and Flight Test
Project Sunrise was a proof-of-concept version of a solar powered aircraft capable of extended flights (months) at altitudes in excess of 100,000 feet. This concept came to fruition 28 years later in 2002 when Project Helios exceeded 100,000 feet altitude.
This project was funded by ARPA (Advanced Research Project Agency) within the Department of Defense. This Funding was channeled through the Lockheed Aircraft Corporation in Sunnyvale California. The contract called for development of a proof of concept aircraft powered solely by incident sunlight on the wing surfaces. Wing span was 32 feet and gross weight was 22 pounds. Wing loading was an astounding of 4 oz. per sq.ft. Power was from an array of solar panels mounted on the aft 2/3 of the wing surface. Construction was of spruce and balsa with maple doublers at the attachment points
Project Sunrise was Conceived by Roland Boucher in 1972 while he was employed by Hughes Aircraft. The concept was disclosed to management and was reviewed by one of Hughes’ aerodynamicists, Bodat Wandzura. Hughes released the concept to Roland Boucher in 1973. A patent was then applied for but was denied.
In 1973 Mr Roland Boucher took a leave of absence from Hughes Aircraft and Joined his Brother Bob Boucher in forming Astro Flight Inc., which up to then was a small model airplane manufacturer located in Venice California. Roland Boucher was its first President and designer of its electrical power systems. In addition to his work on model aircraft motors and batteries he was responsible for the development of the motors and batteries for for an electric powered battlefield drone. This Contract was managed by Bob Boucher under a DARPA contract which was funded through the Northrop Corporation. The drone aircraft flew successfully for one hour carrying a 5 pound payload and was shown on Los Angels television.
IN January 1974, Astro Flight received the long awaited contract to develop Project Sunrise. Roland Boucher resigned the presidency of Astro Flight and devoted his full attention to the development of this project which was funded through the Lockheed Corp. in Sunnvale California Astro Flight rented the loft above its main shop for the Project Sunrise and the program began.
Roland Boucher was responsible for all structural design, aerodynamics, telemetry and control, and something new, navigation, as well as the solar panel, electric motors, gearbox and propeller. Most of the actual construction was performed by Mr. Phil Bernhardt and an associate, both expert model builders with wide experience. Mr. James Odino agreed to provide the R/C transmitters and receivers for both control and telemetry. Henry Radio supplied the amplifier used to boost the power of the R/C hand held control unit, and Heliotech supplied the solar cell arrays.
Structure
Early structural tests using a whiffle tree showed that while balsa wood could be used for tension loads, it would fail completely in shear at the wing attachment points on a 22 pound plane. The final design of the wing spars used spruce spar caps with maple doublers at all attachment points with dual 3/32 balsa shear webs attached to 1/8 x 3/8 hard balsa strips mounted to the upper and lower wing spars. The ribs were 3/32 balsa. This was in effect a balsa box with tapered spruce caps. The leading edge was covered with 1/32 balsa to form a D spar at the leading edge. The trailing edge was formed by two two-inch wide 1/32 sheets forming a triangle with 1/8 x 3/8 vertical spar sections between the ribs. The covering was 1/2 mil Mylar obtained from FAI Model Supply. The result was 32 foot wing which weighed 5 pounds and could handle loads up to 100 pounds.
Aerodynamics
The aerodynamic design of this plane was primarily that of a sailplane. The tail volume coefficient was over 100 percent ensuring a stable climb attitude even when out of sight of ground control. The principal point of concern by the Lockheed team was the reliability of the German model data used in selecting the Eppler 387 airfoil.
The plan was to build a 1/4 scale model of Sunrise and measure its sink rate in calm air. Through the influence of DARPA, one of the giant blimp hangars in Tustin California was set aside for the glide test. The model was hand-launched from a catwalk at the 100 foot level and guided in a circular flight path down to floor level. This was a complete success. A sink rate less than one foot per second was achieved with the 1/4 scale model. This test duplicated the Reynolds number at the expected peak altitude of 78,000 feet. Later, when the 32 foot plane was tested at Bicycle Lake using battery power, both the aerodynamic and propeller performance were confirmed.
Telemetry and Control
Mr. Jim Odino of S&O radio designed and built the telemetry transmitter and receiver. A standard S&O six channel radio was used for control. The control functions were elevator, rudder, motor on/off, and solar cell operating mode (series/ parallel). The telemetry functions were motor current, motor voltage, motor RPM, airspeed, and two heading references from the sun compass. The ground display consisted of four milliammeters displaying current, voltage, RPM, and airspeed, and two zero-center meters displaying sun heading. This was similar to a standard aircraft ILS display.
Navigation
A simple sun compass was used to navigate. It consisted of a small square balsa block about 1 1/2 inches on edge and 3/4 inch thick. the edges were tapered inward with the top square smaller than the bottom. Four solar cells were attached, one to each side.
The cells on opposite sides were connected in opposition and the resulting voltage telemetered to ground. The compass was mounted to the top of the fuselage. It allowed the operator to steer the plane accurately maintaining either wing tip, or the nose or tail aligned to the sun. It weighed less than one ounce.
Astro 40 Cobalt Motor
Two prototype Astro Flight 3/8 Horsepower 40 motors were used during early flight tests with battery power. High altitude flights under solar power required top efficiency and light weight. The ferrite magnets of an Astro 40 were replaced by Samarium Cobalt magnets manufactured by a small company in Watsonville California. The new motor was qualified in a Lockheed altitude chamber to 78,000 feet before installation in the plane. It could produce 3/4 horsepower and was the first motor in the world to use Samarium Cobalt magnets.
Speed Reducer and Propeller
A belt drive was use to reduce motor speed by a 6:1 ratio for both the initial flights on battery power and for all flights on solar power. The Propeller diameter was 30 inches and the pitch 15 inches. At full power the single cobalt motor could turn the prop at nearly 2000 RPM.
Solar Panel
The solar panel consisted of four panels. Two equal main panels were mounted to the inboard constant-chord wing sections, and two smaller panels with half the current and half the voltage mounted to the tapered outer wing panels.
The Solar panels were operated a nominal voltage and 150% current on take-off and at altitudes below 20,000 feet. This was accomplished by activating a relay which connected the outer solar panels in series while connecting the pair in parallel with the main soar panels. This setting increased available motor current by 50 percent over what was available from the main panels alone.
Above 20,000 feet altitude the solar panel would operate at nominal current and 150% voltage. The control relay would now connect the outer panels in
parallel and place the pair in series with the main solar panel. This mode increased available motor voltage by 50 percent. Circular solar cells were used because of cost considerations.
Flight Test on Battery power at Bicycle Lake California
The first flight test was on battery power prior to the attachment of the solar cells. Sunrise was launched by a bungee cord to about a 20 foot altitude, then the electric motor was activated. The plane climbed to about 500 feet by the end of the runway. It then glided in a rectangular pattern turning left to fly crosswind, then left
again to fly downwind, then left again on base leg and finally left again to final approach. On the first pass sunrise still had over 50 feet altitude when passing the operators located about 300 feet down the runway. The power-on portion was reduced gradually until an accurate measure of the average power required was established. This Flight test on battery power was a complete success.
Flight Test on Solar Power at Bicycle Lake california
The solar panels which had been under construction at Heliotech in San Fernando California were mounted, and the electrical power verified with the aircraft in our parking lot. The Aircraft was returned to Bicycle Lake, a final full power check of Solar panel and electric motor was performed, and Sunrise made its first flight powered solely by incident sunlight on the flying surfaces.
The weather was extremely cloudy that year even in the desert, and
for some weeks we would wait in vain for clear skies and low wind. In all, 28 flights were made on solar power alone. Take off was sluggish, but once an altitude of a few thousand feet was achieved, the cells cooled down, power increased and Sunrise maintained a respectable rate of climb. The Telemetry and control system worked flawlessly and navigation by means of the sun compass was demonstrated,
The final flight was made with cumulus clouds covering about 15% of the sky. The pilot flew too close to a cloud at about 8000 feet and Sunrise was destroyed in severe turbulence. We were disappointed that an altitude of 78,000 feet had not been achieved. However, there was no longer any doubt that Project Sunrise had demonstrated the feasibility of solar powered flight to extreme altitudes.
The Designer, Roland Boucher is checking the voltage and current under full power, Col Thacker looks on as Bob Boucher operates the throttle. The little black square about afoot aft of the Wing is the sun compass which weighed less than one oz. Circular solar cells covered a large part of the wing.
The camera man was a Lockheed engineer whose name I seem to have lost. The man on the left is Col Bob Thacker, a well known modeler and former military pilot; the man on the right is my brother Bob Boucher. The aircraft was launched by holding on to piano wires used to stabilize the aircraft on the ground.
These first 28 flights of Project Sunrise demonstrated the feasibility of developing a solar powered plane with unlimited endurance.
Project Sunrise Prototype # 2
The Lockheed project office and DARPA suggested that the excess climb power would be better spent charging a battery for night flight rather than to rely on glide only. Astro Flight was instructed to submit a proposal for a follow on version of the first prototype aircraft.
Roland Boucher prepared a proposal to Lockheed for a follow on version which would use a higher efficiency solar panel. The new solar panels would produce more power, and because they were much were smoother, would produce less aerodynamic drag. This proposal was accepted by Lockheed in the spring of 1975.
Mr Roland Boucher had become mentally and physically exhausted from the strain of developing project Sunrise. He suffered from Congestive Heart failure and was placed in intensive care in Santa Monica Hospital. Before leaving the hospital he resigned from Astro Flight and sold his interest to his brother Bob Boucher. After recuperating for a number of months he returned to Hughes Aircraft Corp.
